1. Field of the Invention
The present invention relates to an image pickup apparatus for photographing a desired area in an image at high image quality, and to a control method for controlling the image pickup apparatus.
2. Description of the Related Art
In known image pickup apparatuses, such as digital cameras and video cameras, functions including auto focus (AF), auto exposure (AE), and auto white balance (AWB) functions are performed on the basis of brightness and color at a predetermined position on the screen.
On the other hand, there is a technique in which a screen is divided into a plurality of areas and, using the average of a pixel value of each area and a threshold value, exposure is controlled by adjusting the exposure to that of areas of low brightness. This technique thus allows backlight compensation regardless of where an object is located (for example, see Japanese Patent Laid-Open No. 2001-249374).
However, this technique does not always ensure that the object can be photographed at high image quality, because the backlight compensation may be performed by adjusting the exposure to that of dark areas outside the object. Therefore, the location and size of the object need to be detected to photograph the object at high image quality.
There are some techniques for detecting and processing an object in an image. For example, there is a technique that uses a neural network to detect an object in an image, and controls exposure using the brightness value of only the area within the detected object (for example, see Japanese Patent No. 2793817). There is another technique that uses a neural network to detect an object in an image, and determines the focus through a hill-climbing servo technique using the brightness value of only the area within the detected object (for example, see Japanese Patent No. 2761391). In addition, there is a technique in which the photographer specifies an object, an area is determined using color information of the object, and auto exposure (AE) and the like are performed using picture signals from the area (for example, see Japanese Patent Laid-Open No. 7-107505).
However, even if an object is detected and the exposure and focus are controlled using only the brightness value of the object, it cannot always be ensured that images of a quality desired by the photographer can be obtained. For example, exposure control performed by adjusting the exposure to that of a backlit object in an image may cause overexposure in an area outside the object within the image. If someone takes photos on a trip, it is normally expected that background scenery, as well as the object, can be photographed with high quality. Therefore, even if clear images of someone and their friend appear on a photo, it cannot be described as a “good” photo unless their background is well photographed.
To solve problems such as those described above, a technique is used to specify the limit of exposure compensation, and maintain an appropriate balance, on the entire screen, between the exposure state of an object selected by the photographer and the exposure state of the surrounding object (for example, see Japanese Patent Laid-Open No. 8-279958). Another technique requires the photographer to roughly define a camera-to-object distance, and allows focusing on a plurality of objects, including the target object, located within a predetermined range around the camera-to-object distance defined by the photographer (for example, see Japanese Patent Laid-Open No. 6-233165). However, this technique requires the photographer to set the location of the object and enter the distance and the like, and thus causes inconvenience for the photographer.